BAGHDAD, May 28 -- Iraq's U.S.-appointed Governing Council on Friday unanimously nominated Ayad Allawi, a Shiite Muslim politician and former exile whose party was supported by the CIA, to be the country's interim prime minister.

The council's selection of Allawi, a physician who left Iraq in 1971, was quickly endorsed by L. Paul Bremer, the U.S. civilian administrator of Iraq, and later by Lakhdar Brahimi, the U.N. representative who is leading efforts to form an interim Iraqi government, council members said. A senior Bush administration official in Baghdad who spoke on the condition of anonymity said Allawi would become Iraq's post-occupation prime minister, the most powerful position in the new government.

Allawi, 58, is regarded by some U.S. officials as a compromise candidate well suited to lead Iraq until national elections early next year. Although he is secular, he reportedly has the support of the country's top Shiite cleric, and he has served as the Governing Council's point man on security issues. He also has welcomed Sunni Muslims and ethnic Kurds into his political organization and promoted reconciliation with former members of Saddam Hussein's Baath Party, a group he supported more than 30 years ago.

But that tie, along with Allawi's links to the CIA and his three-decade absence from the country, could prove controversial among ordinary Iraqis, who remain deeply suspicious of politicians who lived abroad and were backed by Western governments. Almost 14 months after the fall of Hussein's government, public opinion polls indicate that Allawi has not emerged as a widely popular national leader.

There were differing accounts of how Allawi came to be selected by the council and subsequently endorsed by Bremer and Brahimi. The senior administration official said Allawi was recommended by Brahimi after the U.N. envoy conducted numerous meetings with Iraqi political, tribal and religious leaders.

But a U.N. official familiar with the process said Allawi was not Brahimi's top choice. Instead, Allawi lobbied other council members to support his candidacy over the past few weeks, eventually generating enough critical mass to compel the backing of Brahimi and the Bush administration, the official said.

Allawi, a tall man with a round face, made his move after Shiite politicians on the council rejected Brahimi's top choice, nuclear scientist Hussain Shahristani, a Shiite, the official said. Brahimi had wanted a prime minister who, like Shahristani, was not a council member or affiliated with a political party, reasoning that such a person would be best suited to prepare the country for elections. But council members insisted that the prime minister be a leader of a large Shiite political party, council sources said, adding that some members even hinted that they would withhold support for the interim government if Brahimi did not pick a Shiite politician.

When Shahristani withdrew from consideration, the United Nations and the United States were left with three viable choices: Allawi, Adel Abdel-Mehdi of the Supreme Council for the Islamic Revolution in Iraq and Ibrahim Jafari of the Dawa party. All three are members of the Governing Council.

Because the Supreme Council and Dawa are religious parties with almost no non-Shiite members, the official said, Abdel-Mehdi and Jafari were less attractive to Brahimi, Bremer and presidential envoy Robert D. Blackwill, the trio charged with forming the interim government. At the same time, Allawi appeared to be gaining the most support on the council because of his politicking.

"Mr. Brahimi did not pick this candidate," an official involved in the process said. "He simply endorsed a consensus of the Governing Council."

"The name did not come" from the Governing Council, the official said. "It was terrific they endorsed the name, but the name came out of this Brahimi process."

The administration official said Allawi emerged as the leading candidate in the extensive consultations that Brahimi, Bremer and Blackwill had with various groups of Iraqis. "It was just pure democratic politics," the official said. "One candidate got a lot of momentum."

The official said other candidates on Brahimi's list were not "acquiring much support" among Iraqis being consulted. But the U.N. official said most of the consultations involved Governing Council members who had an incentive to choose one of their own.

The Governing Council's acting president, Ghazi Yawar, eventually decided to schedule a special meeting on Friday afternoon to endorse Allawi's candidacy. At the meeting, the normally fractious council unanimously backed Allawi within minutes.